docs: def cumulative_value(self, mag_val, moment_rate, beta, moment_mag):
          '''
          Calculates the cumulative rate of events with M > m0 using
          equation 11 of Youngs & Coppersmith (1985)
  
          :param float mag_val:
              Magnitude
  
          :param float moment_rate:
              Moment rate on fault (in Nm) from slip rate
  
          :param float beta:
              Exponent (b log(10)
  
          :param float moment_mag:
              Moment of the upper bound magnitude
          '''
          exponent = exp(-beta * (self.mmax - mag_val))
          return (moment_rate * (D_VALUE - self.b_value) * (1. - exponent)) /\
              (self.b_value * moment_mag * exponent)